5.2.2 Selection of Best Copy

5.2.2.1 Mechanical recording may be either instantaneous or replicated. The former are mostly unique items, single recordings created of a particular event. These include wax cylinders1,  lacquer (also known as acetate) discs and recordings created by office dictation machines (see 5.2.9). Replicated recordings, on the other hand, are pressed or moulded reproductions of an original master, and are almost always manufactured in multiples. Instantaneous recordings should be identified and treated separately and carefully.

5.2.2.2 Instantaneous cylinders may be distinguished by their waxy appearance and feel, and were generally made of a soft metallic soap. Their colour typically can vary from a light butterscotch to a dark chocolate brown, or very rarely, black. Replicated cylinders were made of a much harder metallic soap, or alternatively of a celluloid sleeve over a plaster core. These were manufactured in a variety of colours, though black and blue were the more common, and usually bear some content information embossed into a flattened end.

5.2.2.3 The first disc format capable of instant replay appeared around 1929. The discs were made of an uncoated soft metal (usually aluminium, possibly copper or zinc) into which a lateral groove was embossed rather than cut, and are easily distinguished from replicated shellac discs. Like the subsequent lacquer discs, the embossed metal format was designed to allow the discs to be replayed on standard gramophones of the time, and so recordings can be loosely categorised as coarse groove and 78 rpm, but the transfer engineer should expect some variation, not least in the groove profile.

5.2.2.4 Lacquer or acetate discs, introduced in 1934, are most frequently described as laminated, although that is not their method of manufacture, or as acetates, which is not the nature of their recording surface. They most commonly consist of a strong and stiff base (aluminium or glass, occasionally zinc) covered with a layer of cellulose nitrate lacquer, coloured dark to improve observation of the cutting process. Rarer are discs which have a cardboard base. The cutting properties are controlled by the addition of plasticisers (softening agents), such as castor oil or camphor.

5.2.2.5 Lacquer discs can appear similar to shellac or more typically vinyl, but they can be distinguished in several ways. The base material can often be seen between the outer lacquer layers, either within the centre hole or at the disc edge.Where the disc has a paper label the content information will often be typed or handwritten rather than printed. On discs without paper labels one or more additional off-centre drive holes may be seen near the centre hole. Though cellulose nitrate lacquer discs on metal or glass base are the most common instantaneous disc, in practice a great variety of other materials were used, such as cardboard as the base media, or gelatine as the recording surface, or as a homogenous recording disc.

5.2.2.6 Due to their inherent instability lacquer discs should be transferred with a high priority.

5.2.2.7 The selection of the best copy, in those circumstances where multiple copies on instantaneous discs exist, is usually a process of determining the most original intact copy of an item. In the case of mass produced mechanical recordings, where the existence of multiple copies is the normal situation, the following guide to selection of best copy applies.

5.2.2.8 Selection of the best copy of replicated mechanical media draws on knowledge of the production of the recording, and the ability to visually recognise wear and damage which would have an audible effect on the signal. The recording industry uses numbers and codes, generally located in the space between the run-out groove and the label in a disc recording, to identify the nature of the recording. This will help the technician determine which recordings are in fact identical, or alternate recordings of the same material.Visual signs of wear or damage are best seen in the way a recording reflects light. To best show the effect an incandescent light is a necessity, generally aimed at the recording from behind the technician’s shoulder, so that they are looking down the beam of light. Fluorescent tubes, or energy saving compact fluorescent lights do not provide the necessary coherent light source to reveal wear and should not be used. A stereoscopic microscope is helpful in assessing groove shape and size, and in examining wear caused by previous replay, which helps selection of the correct replay stylus. A more objective approach involves using a stereo-microscope with a built-in reticule which enables more accurate selection of styli (Casey and Gordon 2007).


1 The earliest commercial wax cylinders were replicated acoustically, one from another, and performers would often do multiple sessions to create batches of similar recordings. They should all be regarded as unique items.